Shaft-mounted detector for optical encoder

ABSTRACT

A transmissive optical encoder is disclosed. The transmissive optical encoder includes a detector, a code wheel, and an emitter. The detector includes an aperture through the detector. The aperture is configured to receive a rotary shaft of a motor. The code wheel is coupled to the rotary shaft of the motor. Rotation of the rotary shaft results in corresponding rotation of the code wheel. The emitter is configured to emit a light signal through the code wheel toward the detector. Rotation of the code wheel results in modulation of the light signal at the detector. Embodiments of the transmissive optical encoder consume relatively little space and facilitate alignment of the emitter and detector.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a divisional of copending application Ser. No. 11/868,508, filedOct. 7, 2007, the entire disclosure of which is incorporated into thisapplication by reference.

BACKGROUND OF THE INVENTION

Optical encoders are used to monitor the motion of, for example, arotary shaft such as a crank shaft. Optical encoders can monitor themotion of a shaft in terms of position and/or number of revolutions ofthe shaft. Optical encoders typically use a code wheel attached to theshaft to modulate light as the shaft and the code wheel rotate. In atransmissive code wheel, the light is modulated as it passes throughtransmissive sections of a track on the code wheel. The transmissivesections are separated by non-transmissive sections. In a reflectivecode wheel, the light is modulated as it is reflected off of reflectivesections of the track on the code wheel. The reflective sections areseparated by non-reflective sections. As the light is modulated inresponse to the rotation of the code wheel, a stream of electricalsignals is generated by a photosensor array that receives the modulatedlight. The electrical signals are used, for example, to determine theposition and/or number of revolutions of the shaft.

FIG. 1 illustrates a conventional transmissive optical encoder system10. The optical encoder system 10 includes an encoder 12 and atransmissive code wheel 14. The code wheel 14 is coupled to a rotaryshaft 16 of a motor 18. The encoder 12 includes a light source 20, acollimating lens 22, and a detector 24. Together, the light source 20and the collimating lens 22 also may be referred to as an emitter. Thelight source 20 emits light, which is collimated by the collimating lens22 and is modulated as it passes through the transmissive sections ofthe code wheel 14. The detector 24 includes a photosensor array such asan array a photodiodes which detects the modulated light. Typically, thephotosensor array has a resolution that is equal to the resolution ofthe coding element.

One disadvantage of conventional transmissive optical encoders, comparedto conventional reflective optical encoders, is that the placement ofthe emitter 20 and the detector 24 on opposite sides of the code wheel14 consumes more space, making the conventional transmissive opticalencoder 12 relatively large. Also, misalignment of the emitter 20 and/orthe detector 24 with the code wheel 14 or with each other degrades theperformance of conventional transmissive optical encoders 12

SUMMARY OF THE INVENTION

Embodiments of a transmissive optical encoder are described. In oneembodiment, the transmissive optical encoder includes a detector, a codewheel, and an emitter. The detector includes an aperture through thedetector. The aperture is configured to receive a rotary shaft of amotor. The code wheel is coupled to the rotary shaft of the motor.Rotation of the rotary shaft results in corresponding rotation of thecode wheel. The emitter is configured to emit a light signal through thecode wheel toward the detector. Rotation of the code wheel results inmodulation of the light signal at the detector. Embodiments of thetransmissive optical encoder consume relatively little space andfacilitate alignment of the emitter and detector. Other embodiments ofthe transmissive optical encoder are also described.

Embodiments of a detector of a transmissive optical encoder are alsodescribed. In one embodiment, the detector includes a substrate and aphotosensor array. The substrate includes an aperture through thesubstrate. The aperture is configured to receive a rotary shaft of amotor. The photosensor array is coupled to the substrate. Thephotosensor array is located on the substrate at a position to receive amodulated light signal from an emitter through a coding element coupledto the rotary shaft. Other embodiments of the detector are alsodescribed.

Embodiments of a method are also described. In one embodiment, themethod is a method for method for assembling transmissive opticalencoder system. The method includes mounting a detector comprising aphotosensor array on a rotary shaft of a motor. The rotary motor shaftprojects through an aperture in the detector. The method also includesmounting a coding element to the rotary shaft to modulate a light signalupon rotation of the rotary shaft. The method also includes mounting anemitter relative to the coding element to generate the light signal andto direct the light signal toward the coding element. The detector islocated to detect the modulated light signal. Other embodiments of themethod are also described.

Other aspects and advantages of embodiments of the present inventionwill become apparent from the following detailed description, taken inconjunction with the accompanying drawings, illustrated by way ofexample of the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a conventional transmissive optical encoder system.

FIG. 2 depicts a schematic block diagram of one embodiment of atransmissive optical encoding system mounted directly on a shaft of amotor.

FIG. 3A depicts a schematic perspective view of one embodiment of arectangular detector for use in the optical encoder of FIG. 2.

FIG. 3B depicts a schematic top view of one embodiment of a rectangulardetector with a circular photosensor array which circumscribes theaperture that extends through the detector.

FIG. 4 depicts a schematic perspective view of another embodiment of arectangular detector with an offset aperture for use in the opticalencoder of FIG. 2.

FIG. 5 depicts a schematic perspective view of another embodiment ofrectangular detector with chamfered corners for use in the opticalencoder of FIG. 2.

FIG. 6 depicts a schematic perspective view of one embodiment of acircular detector for use in the optical encoder of FIG. 2.

FIG. 7 depicts a schematic circuit diagram of one embodiment of anoptical encoder for use in the transmissive optical encoder system ofFIG. 2.

FIG. 8 depicts a partial schematic diagram of one embodiment of a codewheel.

FIG. 9 depicts a schematic layout of one embodiment of a photosensorarray relative to the code wheel track.

FIG. 10 depicts a schematic flow chart diagram of one embodiment of amethod for assembling the transmissive optical encoder system of FIG. 2.

FIG. 11 depicts a schematic flow chart diagram of one embodiment of amethod for making a detector for the optical encoder of FIG. 2.

FIG. 12 depicts a schematic block diagram of another embodiment of thetransmissive optical encoding system of FIG. 2.

Throughout the description, similar reference numbers may be used toidentify similar elements.

DETAILED DESCRIPTION

FIG. 2 depicts a schematic block diagram of one embodiment of atransmissive optical encoding system 50 mounted directly on a shaft 16of a motor 18. The illustrated transmissive optical encoding system 50includes a code wheel mounting device 52 to mount a code wheel 54 to theshaft 16 of the motor 18. Any type of conventional code wheel mountingdevice 52 may be used. In some embodiments, the code wheel 54 may be anytype of conventional transmissive code wheel 54. Some exemplary codewheels 54 are describe in U.S. Pat. Nos. 4,451,731, 4,691,101, and5,241,172, which are incorporated by reference herein. Other code wheels54 also may be used. At least one embodiment of a code wheel 54 isdescribed in more detail below, referring to FIG. 8.

The illustrated transmissive optical encoding system 50 also includes aflexible circuit 56. An emitter 60 is mounted to the flexible circuit 56at a location that allows the emitter 60 to emit a light signal (shownas arrows) toward the motor 18 through the code wheel 54. Otherembodiments may use a rigid circuit or other connection in place of theflexible circuit 56 shown and described herein. For example, wires maybe used in place of the flexible circuit 56. Some embodiments alsoinclude a collimating lens 62 to collimate the light from the emitter 60prior to transmission through the code wheel 54. Various types ofemitters 60 and collimating lenses 62 are known.

The illustrated optical encoding system 50 also includes a detector 64.The detector 64 is mounted to the flexible circuit 56 at a location toreceive the light signal from the emitter 60, after the light signalpasses through the code wheel 54. Exemplary embodiments of the detector64 include integrated circuit (IC) dice and IC packages. Althoughvarious types of detectors 64 may be used, the depicted detector 64includes a substrate 66 and a photosensor array 68. Some embodiments ofthe detector 64 also include a package to enclose, or house, thesubstrate 66 and the photosensor array 68. In one embodiment, thephotosensor array 68 is circular so that it circumscribes the shaft 16of the motor 18. One example of a circular photosensor array 68 is shownin FIG. 3B and described in more detail below. Other embodiments ofphotosensor arrays also may be implemented.

In order for the light to reach the photosensor array 68 within thepackage, the detector 64 may include a substantially transmissive window69 that is aligned with the photosensor array 68. For example, if acircular photosensor array 68 is implemented, then the window may becircular 69 to substantially correspond to the circular photosensorarray 68. In this way, the photosensor array 68 is able to receive thelight from the emitter 60 that transmits through the code wheel 54. Inan alternative embodiment, the package may include a cutaway window,instead of the transmissive window 69, so that there is no structure toimpede or otherwise modify the path of the light signal from the codewheel 54. In another embodiment, the photosensor array 68 may beapproximately flush with the package at the incident surface of thedetector 64. In another embodiment, the photosensor array 68 may extendout of the package of the detector 64. In another embodiment, thedetector 64 may be implemented without a package, so there is no needfor a transmissive window 69 or other portion to allow the light signalto be incident on the photosensor array 68.

Regardless of the type of detector technology implemented, the detector64 includes an aperture, or hole, that extends through the detector 64.In other words, there is an aperture through the substrate 66 and, wherea package is used to house the substrate 66, there is a correspondingaperture through the package. The presence of the aperture through thedetector 64 allows the rotary shaft 16 of the motor 18 to extend throughthe detector 64. In other words, the detector 64 is mounted eccentric tothe motor shaft 16 of the motor 18.

In one embodiment, the aperture approximately corresponds in size withthe motor boss (the plastic structure that surrounds the motor shaft 16as it protrudes from the housing of the motor 18. This embodimentmaintains a separation between the shaft 16 and the detector 64 so thatthe shaft 16 does not create friction on the detector 64 as the shaft 16rotates. Alternatively, the detector 64 may be mounted to the housing ofthe motor 18 using a centering jig to maintain the separation betweenthe shaft 16 and the detector 64.

The size (i.e. diameter) of the aperture may vary depending on theimplementation for which the detector 64 is designed. In someembodiments, the aperture may be just large enough, within a measurabletolerance, to allow the shaft 16 to extend through the detector 64. Inother embodiments, the aperture may be sized, within a tolerance, to fitaround a portion of the motor housing near the shaft 16. Where theaperture is sized to fit relatively closely to the shaft or thecorresponding portion of the motor housing, the placement of thedetector 64 on the shaft 16 may facilitate the proper alignment of theemitter 60 with the photosensor array 68 of the detector 64.Additionally, the aperture may facilitate alignment of the emitter 60and/or the photosensor array 68 of the detector 64 with the code wheel54. In other embodiments, the aperture may be substantially larger thanthe shaft 16 of the motor 18 to facilitate easy assembly of thetransmissive optical encoding system 50.

It should also be noted that at least some embodiments of thetransmissive optical encoding system 50 include a housing (not shown)for the optical encoder. In this way, the optical encoder may beprotected from potentially harmful operating conditions such as dust,dirt, ink, or other particulate matter, depending on the application inwhich the optical encoder is implemented.

FIG. 3A depicts a schematic perspective view of one embodiment of arectangular detector 64 for use in the optical encoder of FIG. 2. Inparticular, the package of the rectangular detector 64 is shown, and thesubstrate 66 and photosensor array 68 are mounted within the package.The illustrated rectangular detector 64 includes an aperture 70 thatextends through the entire structure of the detector 64, including thesubstrate 66 and the package. Although the photosensor array 68 and thewindow 69 are not shown in FIG. 3A, FIG. 3B depicts a schematic top viewof one embodiment of a rectangular detector 64 with a circularphotosensor array 68 which circumscribes the aperture 70 that extendsthrough the detector 64. In the depicted photosensor array 68 of FIG.3B, the individual photodiodes are distinguished. Also, it should benoted that, although embodiments of an incremental encoder are shown anddescribed herein, other embodiments of the transmissive optical encodersystem 50 may implement other types of encoders, including anincremental encoder for multiple channels, a commutation encoder withmultiple channels, a pseudo-absolute encoder, an absolute encoder, oranother type of encoder. Additional details of the functionality of thephotosensor array 68 are described in more detail below with referenceto FIG. 9.

Although the aperture 70 is shown with a substantially circularcross-section, other embodiments of the detector 64 may have apertureswith other shapes and sizes of apertures. For example, some embodimentsof the detector 64 include apertures 70 with rectangular, square,triangular, or oval cross-sections. Other embodiments of the detectorinclude apertures 70 with non-canonical shapes, for example, to conformto the shape of an extended portion of the motor housing. Additionally,other embodiments include more than one aperture, in order toaccommodate multiple structures (e.g., the shaft 16) extending throughthe detector 64.

FIG. 4 depicts a schematic perspective view of another embodiment of arectangular detector 72 with an offset aperture 74 for use in theoptical encoder of FIG. 2. Although the shape and size of the aperture74 is substantially similar to the shape and size of the aperture 70 ofthe detector 64 shown in FIG. 3, the aperture 74 is offset so that it iscloser to one edge of the detector 72. This embodiment may facilitate asimpler layout for the circuitry within the detector 72, compared to thedetector 64 of FIG. 3.

FIG. 5 depicts a schematic perspective view of another embodiment ofrectangular detector 76 with chamfered corners for use in the opticalencoder of FIG. 2. The corners of the rectangular detector 76 arechamfered so that the overall space consumption of the detector 76 issmaller compared to a rectangular detector of the same size withoutchamfered corners. Embodiments with chamfered corners may conform betterto cylindrical housings of certain motors.

FIG. 6 depicts a schematic perspective view of one embodiment of acircular detector 78 for use in the optical encoder of FIG. 2. Inparticular, the circular detector 78 has a cylindrical shape. Like therectangular detector 76 with chamfered corners, the circular detector 78may conform better to cylindrical housings of certain motors. Usingdifferent shapes for different implementations may provide increaseddetector area in the relatively small application areas. In other words,different shapes of detectors allow the optical encoder to fit intosmall form factor implementations.

FIG. 7 depicts a schematic circuit diagram of one embodiment of anoptical encoder 100 for use in the transmissive optical encoder system50 of FIG. 2. The illustrated transmissive optical encoding system 100includes a code wheel 104, an encoder 106, a decoder 108, and amicroprocessor 110. The code wheel 104 is substantially similar to thecode wheel 54 of FIG. 2. Although a more detailed illustration of thecode wheel 104 is provided below with reference to FIG. 8, a briefexplanation is provided here as context for the operation of thetransmissive optical encoding system 100 shown in FIG. 7.

In general, the code wheel 104 includes a track 140 of transmissivesections 142 and non-transmissive sections 144. An emitter 120 in theencoder 106 produces light (i.e., a light signal) that is incident onthe code wheel track 140. As the code wheel 104 is rotated, for exampleby a motor shaft 16, the incident light is transmitted through the codewheel 104 by the transmissive sections 142 of the track 140, but is nottransmitted by the non-transmissive sections 144 of the track 140. Thus,the light is transmitted through the track 140 in a modulated pattern(i.e., on-off-on-off . . . ). A detector 130 in the encoder 106 detectsthe modulated light signal and, in response, generates one or moreperiodic channel signals (e.g., CH_(A) and CH_(B)). In one embodiment,these channel signals are then transmitted to the decoder 108, whichgenerates a count signal and transmits the count signal to themicroprocessor 110. The microprocessor 110 uses the count signal toevaluate the movement of, for example, the motor shaft 16 or othermoving part to which the code wheel 104 is coupled. Other embodimentsmay implement other types of code wheels 104, such as multi-track andabsolute position code wheels, as are known in the art.

In one embodiment, the encoder 106 includes the emitter 120 and thedetector 130. The emitter 120 includes a light source 122 such as alight-emitting diode (LED). For convenience, the light source 122 isdescribed herein as an LED, although other light sources, or multiplelight sources, may be implemented. In one embodiment, the LED 122 isdriven by a driver signal, V_(LED), through a current-limiting resistor,R_(L). The details of such driver circuits are well-known. Someembodiments of the emitter 120 also may include a collimating lens 124(substantially similar to the collimating lens 62 of FIG. 2) alignedwith the LED 122 to direct the projected light in a particular path orpattern. For example, the collimating lens 124 may direct approximatelyparallel rays of light onto the code wheel track 140.

In one embodiment, the detector 130 includes one or more photosensors132 such as photodiodes. The photosensors 132 may be implemented, forexample, in an integrated circuit (IC). For convenience, thephotosensors 132 are described herein as photodiodes, although othertypes of photosensors 132 may be implemented. In one embodiment, thephotodiodes 132 are uniquely configured to detect a specific pattern orwavelength of transmitted light. In some embodiments, severalphotodiodes 132 may be used to detect modulated light signals frommultiple tracks 140, including positional tracks and index tracks, or acombined position and index track. Also, the photodiodes 132 may bearranged in a pattern that corresponds to the radius and design of thecode wheel 104. The various patterns of photodiodes 132 are referred toherein as a photosensor array.

The electrical signals produced by the photodiodes 132 are processed bysignal processing circuitry 134 which generates the channel signals,CH_(A) and CH_(B). The signal processing circuitry 134 also may generateother signals, including other channel signals, complementary channelsignals, or an indexing signal, which may be used to determine therotational position or the number of rotations of the code wheel 104.

In one embodiment, the detector 130 also includes one or morecomparators (not shown) to facilitate generation of the channel signals.For example, analog signals (and their complements) from the photodiodes132 may be converted by the comparators to transistor-transistor logic(TTL) compatible, digital output signals. In one embodiment, theseoutput channel signals may indicate count and direction information forthe modulated light signal.

Additionally, the encoder 106 may include a detector lens 136 to directthe modulated light signal toward the photodiodes 132. In oneembodiment, the detector lens 136 is mounted in front of the detector130 for better light extraction and to ensure sufficient power deliveryonto the detector 130. Various embodiments of the detector lens 136 maybe implemented, as described below.

Additional details of emitters, detectors, and optical encoders,generally, may be referenced in U.S. Pat. Nos. 4,451,731, 4,691,101, and5,241,172, which are incorporated by reference herein.

FIG. 8 depicts a partial schematic diagram of one embodiment of a codewheel 104. In particular, FIG. 8 illustrates a portion of a circularcode wheel 104 in the shape of a disc. In some embodiments, the codewheel 104 may be in the shape of a ring, rather than a disc. Theillustrated code wheel 104 includes a track 140, which may be a circulartrack that is concentric with the code wheel 104. In one embodiment, thetrack 140 includes a continuous repeating pattern that goes all the wayaround the code wheel 104. The depicted pattern includes alternatingtransmissive sections 142 and non-transmissive sections 144, althoughother patterns may be implemented. In one embodiment, the transmissivesections 142 are transparent sections of the code wheel 104 or,alternatively, voids (e.g., holes) in the code wheel 104. Thenon-transmissive sections 144 are, for example, opaque sections in thecode wheel 104 or, alternatively, reflective sections in the code wheel104. In one embodiment, the surface areas corresponding to thenon-transmissive sections 144 are coated with an absorptive material.

In another embodiment, a circular coding element 104 may be implementedwith a spiral bar pattern, as described in U.S. Pat. No. 5,017,776,which is incorporated by reference herein. Alternatively, other lightmodulation patterns may be implemented on various shapes of codingelements.

As described above, rotation of the code wheel 104 and, hence, the track140 results in modulation of the transmitted light signal at thedetector 130 to measure positional changes of the code wheel 104. Otherembodiments of the code wheel 104 may include other tracks such asadditional positional tracks or an index track, as are known in the art.

In the depicted embodiment, the transmissive and non-transmissive tracksections 142 and 144 have the same circumferential dimensions (alsoreferred to as the width dimension). In other words, the intermediatenon-transmissive track sections 144 have the same width dimension as thetransmissive track sections 142. The resolution of the code wheel 104 isa function of the width dimensions (as indicated by the span “x”) of thetrack sections 140 and 142. In one embodiment, the width dimensions ofthe non-transmissive track sections 144 are a function of the amount ofarea required to produce a detectable gap between consecutive,transmitted light pulses. The radial, or height, dimensions (asindicated by the span “y”) of the transmissive and non-transmissivetrack sections 140 and 142 are a function of the amount of area requiredto generate a sufficient amount of photocurrent (e.g., the morephotocurrent that is required, the larger the area required and hencethe larger “y” needs to be since area equals “x” times “y”). Typically,the “y” dimension is made substantially larger than the height of thephotodiodes 132.

FIG. 9 depicts a schematic layout of one embodiment of a photosensorarray 150 relative to the code wheel track 140. The photosensor array150 is also referred to as a photodiode array. A representation of thecode wheel track 140 is overlaid with the photosensor array 150 todepict exemplary dimensions of the individual photosensor array elements(i.e., photodiodes 132) with respect to the sections of the code wheeltrack 140. Although the photodiode array 150 corresponds to a circularcode wheel track 140, other embodiments may implement a photosensorarray 150 arranged to align with a linear track of a linear code strip.

The illustrated photodiode array 150 includes several individualphotodiodes, including an A-signal photodiode 152 to generate an Asignal, a B-signal photodiode 154 to generate a B signal, an A/-signalphotodiode 156 to generate an A/signal, and a B/-signal photodiode 158to generate a B/signal. For clarification, “A/” is read as “A bar” and“B/” is read as “B bar.” This designation of the position photodiodes152, 154, 156, and 158 and the corresponding electrical signals that aregenerated by the position photodiodes 152, 154, 156, and 158 iswell-known in the art. The circumferential dimensions (also referred toas the width dimensions, indicated by the span “w”) of the positionphotodiodes 152, 154, 156, and 158 are related to the width dimensionsof the position track sections 142 and 144 of the corresponding codewheel track 140. In the embodiment of FIG. 9, each position photodiode152, 154, 156, and 158 has a width that is one half the width of thetransmissive and non-transmissive track sections 142 and 144 of thecorresponding position track 140 (i.e., “w” equals “x/2”). Otherembodiments of the photosensor array 150 may include other photosensors132, as are known in the art.

FIG. 10 depicts a schematic flow chart diagram of one embodiment of amethod 170 for assembling the transmissive optical encoder system 50 ofFIG. 2. Although specific reference is made to the transmissive opticalencoding system 50 of FIG. 2, some embodiments of the method 170 may beimplemented in conjunction with other optical encoding systems.

At block 172, a detector 64 is mounted to a motor shaft 16. As explainedabove, the detector 64 includes an aperture for a rotary shaft 16 toextend through the aperture of the detector 64. The detector 64 is alsomounted to receive light from an emitter 60, which may be mounted afterthe detector 64 is mounted to the motor shaft 16. At block 174, a codingelement such as a code wheel 54 (or the code wheel 104) is mounted tothe rotary shaft 16. Upon rotation of the rotary shaft 16, the codewheel 54 rotates and, hence, modulates the light signal incident at thedetector 64. In this way, the detector 64 detects the modulated lightsignal from the emitter 60 through the code wheel 54 during operation ofthe transmissive optical encoder system 50.

At block 176, an emitter 60 is provided. The emitter 60 is configured togenerate a light signal. One example of an emitter 60 is a LED, whichmay be coupled to a collimating lens 62, although other types of lightsources may be implemented. In one embodiment, the emitter 60 ismounting to a housing or other structure to hold the emitter 60. Thedepicted method 170 then ends.

Although the operations of the illustrated method 170 are shown anddescribed in a particular, it should be noted that some embodiments ofthe method 170 implement the operations in another order. For example,some embodiments may implement multiple operations at substantially thesame time, for example, by mounting a pre-assemble circuit to the motorshaft 16.

FIG. 11 depicts a schematic flow chart diagram of one embodiment of amethod 180 for making a detector 64 for the optical encoder of FIG. 2.Although specific reference is made to the optical encoder of FIG. 2,some embodiments of the method 180 may be implemented in conjunctionwith other optical encoders.

At block 182, an aperture is formed through a substrate 66. At block184, the photosensor array 68 is mounted on the substrate 66. As usedherein, the term mounting may refer to joining two structures, but isnot necessary limited to joining or coupling separate structurestogether. Mounting also may include fabricating one structure fromanother structure. In one embodiment, the aperture and the photosensorarray 68 are formed in the substrate 66 during wafer fabrication for anIC or IC package. By forming the aperture during wafer fabrication, thelocation of the photosensor array 68 relative to the aperture can beprecisely dimensioned and positioned on the substrate 66. Hence, directmounting such a substrate 66 to the rotary shaft 16 can reduce tolerancestack-up. Since radial and tangential mismatch can affect theperformance of the detector 64 in a small optical radius system, precisealignment of the photosensor array 68 relative to the rotary shaft 16and, hence, the code wheel 54 is beneficial. Such precise positioningalso may enable increased encoder resolution because the photodiodetracks may be packed closely together.

At block 186, the substrate 66 is mounted within a package. The packagehas an aperture corresponding to the aperture in the substrate 66. Thus,the apertures of the substrate 66 and the package align to allow therotary shaft 16 to extend through the detector 64. It should be noted,however, that some embodiments of the detector 64 may be implementedwithout the use of a separate detector package. In fact, the detector 64may be implemented using a variety of technology. An exemplaryimplementation for the detector 64 includes, but is not limited to, ICdice with normal wire bonding & encapsulation to protect the wire bonds.Another exemplary implementation for the detector 64 includes a flipchip with underfill to protect the ball bond. Another exemplaryimplementation for the detector 64 includes a chip-scale-package (CSP)or any other IC packaging. Other types of detectors also may beimplemented.

At block 188, the package is mounted to a flexible circuit 56. At block190, an emitter 60 is also mounted to the flexible circuit 56. In oneembodiment, the emitter 60 is mounted to the flexible circuit 56 in aposition to direct a light signal from the emitter 60 toward thephotosensor array 66 of the detector 64. Alternatively, the flexiblecircuit 56 may be arranged in another manner to direct the light signalfrom the emitter 60 toward the photosensor array 66 of the detector 64.The depicted method 180 then ends.

FIG. 12 depicts a schematic block diagram of another embodiment of thetransmissive optical encoding system 50 of FIG. 2. In contrast to thetransmissive optical encoding system 50 of FIG. 2, the illustratedtransmissive optical encoding system 50 shown in FIG. 12 includes anintegrated circuit (IC) 192 with an integrated photosensor array. Inthis way, the photosensor array is integrated into one chip 192 with thecircuitry. Accordingly, the bare chip 192 can be die attached and wirebonded onto the flexible cable 56 (or another substrate). In oneembodiment, the chip 192 has an axial through hole in order to bemounted on the motor shaft 16. In some implementations, this embodimenttakes up a relatively small area of silicon, so it is feasible to mountthe transmissive optical encoding system 50 on a small motor 18.Additionally, similar to the detector 64 described above, the chip 192may be square, square with chamfered corners, round, or another shapeconducive to mounting on a particular motor 18. Other embodiments mayuse other packaging such as chip scale packaging (CSP), quad flatno-lead (QFN), or another type of transparent package. In allembodiments, the packages include an axial though hole in order to mountthe transmissive optical encoder 50 on the motor shaft 16.

It should be noted that various forms of the optical encoder describedherein may be implemented in several types of applications. For example,some embodiments of the optical encoder may implement an incrementalencoder for two or three channels, or another number of channels. Otherembodiments of the optical encoder may implement a commutation encoderwith six channels, or another number of channels. Other embodiments ofthe optical encoder may implement a pseudo absolute encoder. Otherembodiments of the optical encoder may implement an absolute encoder.Other embodiments of the optical encoder may implement other types ofencoders.

Additionally, the various embodiments of the optical encoder may presentone or more benefits. For example, some embodiments facilitate theimplementation of a relatively small form factor to fit small rotarysystems. Miniaturization may be further applicable with the advancementof smaller transistor sizes in semiconductors. As another example, someembodiments enable a transmissive system for high frequencyapplications, without sacrificing the overall size of the transmissiveoptical encoder. As another example, some embodiments reduce oreliminate positional errors resulting from eccentricity. As anotherexample, some embodiments enable simplicity in top-down assembly of atransmissive optical encoder. Other embodiments may provide other usesand benefits.

Although the operations of the method(s) herein are shown and describedin a particular order, the order of the operations of each method may bealtered so that certain operations may be performed in an inverse orderor so that certain operations may be performed, at least in part,concurrently with other operations. In another embodiment, instructionsor sub-operations of distinct operations may be implemented in anintermittent and/or alternating manner.

Although specific embodiments of the invention have been described andillustrated, the invention is not to be limited to the specific forms orarrangements of parts so described and illustrated. The scope of theinvention is to be defined by the claims appended hereto and theirequivalents.

What is claimed is:
 1. An apparatus comprising: a detector of a transmissive optical encoder, the detector comprising: a circuit substrate comprising an aperture through the circuit substrate, the aperture to receive a rotary shaft of a motor; and a photosensor array coupled directly to a surface of the circuit substrate, the photosensor array located on the circuit substrate at a position to receive a modulated light signal from an emitter through a coding element coupled to the rotary shaft.
 2. The apparatus of claim 1, the detector further comprising a package to substantially enclose the photosensor array and the circuit substrate, wherein the package comprises an aperture through the package, wherein the apertures through the circuit substrate and the package are aligned to receive the rotary shaft of a motor.
 3. The apparatus of claim 2, wherein the detector comprises a substantially rectangular package.
 4. The apparatus of claim 3, wherein the substantially rectangular package comprises a chamfered corner.
 5. The apparatus of claim 2, wherein the detector comprises a substantially cylindrical package.
 6. The apparatus of claim 2, wherein the package further comprises a transmissive window, wherein the transmissive window is aligned with the photosensor array.
 7. The apparatus of claim 2, wherein the package further comprises a cutaway window, wherein the cutaway window is aligned with the photosensor array, wherein the cutaway window has no structure to modify a path of a light signal from the code wheel to the photosensor array.
 8. The apparatus of claim 7, wherein a top surface of the photosensor array is flush with a top surface of the package.
 9. The apparatus of claim 7, wherein at least a portion of the photosensor extends out of the package.
 10. The apparatus of claim 1, wherein the aperture through the circuit substrate is approximately centered on a surface of the circuit substrate.
 11. The apparatus of claim 1, wherein the aperture through the circuit substrate is off-center on a surface of the circuit substrate.
 12. The apparatus of claim 1, wherein the photosensor array circumscribes the aperture through the circuit substrate on the surface of the circuit substrate.
 13. The apparatus of claim 1, wherein the aperture through the circuit substrate continues through an entire thickness of the detector.
 14. The apparatus of claim 1, wherein the photosensor array comprises a circular photosensor array.
 15. The apparatus of claim 14, the detector further comprising a package to at least partially enclose the circuit substrate, wherein the package comprises an aperture through the package to receive the rotary shaft of the motor.
 16. The apparatus of claim 15, wherein the package comprises a circular window aligned with the circular photosensor array. 